1. Field of the Invention
The present invention relates to paraffin wax compositions which can prevent degradation of rubber articles with ozone and afford excellent appearance upon the rubber articles over a wide temperature range from a low temperature zone to a high temperature zone. The invention also relates to rubber compositions into which such paraffin wax compositions are incorporated.
2. Description of the Related Art
In order to prevent rubber from being cracked with air or sun light, it is formerly known that a wax-based antioxidant is used in rubber.
When the wax-based antioxidant is blended with rubber, the antioxidant oozes out onto the surface of rubber and forms a thin film thereon. This thin film prevents the rubber from contacting ozone, and thus prevents degradation thereof.
Although a variety of wax-based rubber antioxidants have been commercially available for a long time, the function of the antioxidant to ooze out and form a thin film and a phenomenon that the thin film once formed is peeled and dropped differ depending upon temperatures. Under the circumstances, in order to improve these problems, there are proposed antioxidants in which the number of the carbons of a wax-based rubber antioxidant is distributed over a wide range of 16-41 (U.S. Pat. No. 3,423,348) and antioxidants containing 25-70% by weight straight chain hydrocarbons having the number of carbons of 26-29 and 30-75% by weight straight chain hydrocarbons having the number of carbons of 34-40 (Japanese patent publication No. 54-25,062).
Japanese patent application Laid-open Nos. 48-91,141 and 63-145,346 disclose wax-based rubber antioxidants having a so-called two peak distribution consisting of greater amounts of wax components having the number of carbons of 26-29 and a wax component having the number of carbons of 34-40 and a smaller amount of a wax component having the number of carbons of 30-33.
Further, Japanese patent application Laid-open No. 1-230,648 discloses antioxidants capable of improving ozone resistance at relatively high temperatures by increasing the content of normal saturated hydrocarbons having the number of carbons of 36-51.
However, the above-mentioned conventional wax-based antioxidants all damage the appearance of rubber articles, and have poor ozone resistance at relatively low temperatures. Therefore, they are unsuitable for rubber compositions which are to be used under conditions of much ozone even at low temperatures and thus highly required to improve ozone resistance.